1. Field of the Invention
This invention relates to electrical switching apparatus and, more particularly, to circuit breakers employing a trip unit. The invention also relates to circuit breaker trip units.
2. Background Information
Circuit breakers and circuit breaker trip units are well known in the art. See, for example, U.S. Pat. Nos. 5,910,760; and 6,144,271.
Resetting of a circuit breaker (e.g., through the operating handle and operating mechanism thereof) is accomplished in a manner well known in the art and is described and shown, for example, in U.S. Pat. No. 5,910,760.
As disclosed in U.S. Pat. No. 6,144,271, a linear plunger of the trip unit is employed to trip open the associated circuit breaker frame whenever the linear plunger is extended from the trip unit. Actuation of primary and secondary frame latches occurs exclusively by way of the extended and resetable trip unit linear plunger, which is, otherwise, normally contained entirely within the trip unit. The secondary frame latch is in disposition to be struck by an abutment surface of the extended linear plunger. In response to a reset operation, the trip unit is also reset whenever the secondary frame latch drives the extended linear plunger in the opposite direction against its plunger spring and into the trip unit.
When a design is dependent upon ensuring that a component travels a required distance, excess travel is designed into the system, called overtravel. Overtravel usually involves a component suspended by springs, in order to allow movement when rotating or translating parts interfere. Such springs require special treatment in the design of their supporting parts and, also, add to manufacturing costs (e.g., the labor cost to install the springs).
There is a need for an improved circuit breaker employing a trip unit.
There is also a need for an improved circuit breaker trip unit.